And by now its obvious that it is used to described someone who is a cross between a moron and less obviously the I.R.Baboon character from the cartoon network show "Cow and Chicken" in 1997 and "I am Weasel" from 1999.
I Am Weasel feature's the adventures of the title character, a highly intelligent mammal, and his constant, albeit stupid rival/partner, I. R. Baboon. The two are often competing in different "humorous" situations, with ‘I. R.’ trying to out-do Weasel at every turn. However, I. M. Weasel, the world renowned professional of everything, always seems to come out on top.
I.R.Baboon was basically a super idiotic red-butted baboon who did everything Wrong and Ass Backwards. The show was lame and the baboon worse but its a description i feel fits many people, especially coupled with Moron.
Jackie: You don’t leave the applicator in when you use a tampon!!!
Megan: Oh is that why it doesn’t feel right?
Jackie: YOU ARE SUCH A MOROON!! How you manage to dress yourself is still a mystery to me!